Thermostat



July' 24, 1928. 1,678,407

J. A. SPENCER THERMOSI'AT Filed Nov. 10, 1925 sheet of steel or otherstiff elastic material.

Patented July 24, 1928.

UNITED STATES PATENT OFFICE.

JOHN A. SPENCER, OF REVERE, MASSACHUSETTS, ASSIGNOR TO SPENCERTHERMOS'IAT COMPANY, OF CAMBRIDGE, MASSACHUSETTS. A CORPORATION OFMASSACHUSETTS.

THERMOSTAT.

Application filed November 10, 1923. Serial No. 673,960.

Objects of the invention are to amplify and abruptly accelerate theresponseof a thermostat at a predetermined temperature; to provide athermostat capable of directly breaking a circuit carrying a relativelylarge current; and to provide a generallyimproved form of thermostat.

In my prior Patent 1,448,240 I have disclosed a thermostat having acupped sheet which is bimetallic and which snaps back and forth betweenhot and cold positions by virtue of the stresses resulting from un-,equal expansion and contraction of its constltuent parts. According tothe present invention external forces are employed to set up internalstresses in the cupped or dented sheet so that the sheet need not beformed of two metals but maybe formed of a single The external forcesmay be'applied by any suitable thermostatic means as for example twoelements having different coefficients of expansion. The thermostaticmeans are arranged to apply said forces to the sheet in suchmanner asto. tend to flex a portion 1 thereof, preferably aportion less than'the.

whole, in the direction opposite to the normal flexure. These forces maybe applied by pressinga portion of the sheet against an abutement whichis offset relatively to the line of the force. When using two ele, mentsas aforesaid one element may be connected to the sheet and the otherelement may serve directly or indirectly as the abut ment against whlchthe sheet is pressed by the first element. The depth of the dent. (orcup) and the elasticity of the sheet are so correlated that when aportion of the dent is flexed as aforesaid the internal stressesultimately reach a condition of instability whereupon the sheet snapsinto a new position. The' dent may be so con structed that. the sheetremains in the new position until other external forces are ap pliedthereto but it is preferably sufliciently shallow and stiff to return tonormal-position when the deforming forces are removed.

Figs. 1 and 2 are elevations partly in section of one embodiment showingthe parts in hot and cold positions respectively;

Fig. 3 is a plan of the thermostat of Figs.

land 2;

' I 0 p 0 Figs. 4 and 5 are views similar to Figs.

1 and 2' showing a modification; and

Fig. 6 i's-an enlarged view illustrating, in

exaggerated form, the operation of the devices.

The particular embodiment shown in Fl 1 to 3 comprises a tube. 11 havingan enlarged upper end 17, a rod 13 extending through the tube andconnected to the tube at the lower end, a downwardly cupped disk 15fastened on the upper end of rod 13 by nuts 14 and overhanging theenlarged upper. end of tube 13, aplate 16 fast to the tube 11 and havingtwo peripheral flanges 18 overhanging the disk 15, electrical contacts19 insulated in plate 16 near the periphery of the diskQlfi, andconductors 20 leading from contacts 19 respectively.

Thetube 11 and rod 13 are formed of materials having differentcoefficients of expansion, for example aluminum and iron respectively,so that when heated the tube expands faster than the rod. The disk 15may be formed by stamping while cold a flat sheet of tempered steel intocupped form. The thickness of the sheet and the set (that is the normalcurvature) should be proportioned in accordance with the conditions,particularly the temperature ranges, in which the device is to be used;for use in flat-irons operating within a temperature range ofapproximately 450 F. to 500 FQthe stock may be of the order of fifteenthousandths of an inch thick and the depth of the cup may beapproximately seventy thousandths of an inch.

' When the device is relatively cold the disk juxtaposed to the flange17. As the device is heated the tube 11, which expands more rapidly thanrod 13, pushes downwardly upon the lower end of the rod and the rod inturn' pulls downwardly upon the center of the disk, the upper end of thetube acting directly as an abutment against which the disk is pressed.During the continuance of this action the periphery'of the disk remainsin contact with terminals 19 until a predetermined temperature isreached, whereupon the eriphery of the disk suddenly snaps'upwardly tothe position shown in Fig. 2, thereby abruptly opening the circuitthrough conductors 20, contacts 19' and disk 15..

While the varying stresses in the cupped disk during the above actionare, because of their complexity, diflicult to analyze, the followin isbelieved to be a correct outline of t e general character of the action.

When the center of the disk is pulled down wardly against the annularabutment the portion of .the disk inside the rib is flexed downwardlycontrarywise to the normal flexure, as illustrated in Fig. 6. Thiscontrary flexing stretches the upper side of the disk and compresses,the lower side and since this flexure tends to flatten the centralportion of the disk, it creates a circumferential tension in thesurrounding portion. When the disk is thus flexed to a certain extent,these mitted to spring upwardly in the middle in response. to saidstresses. At first this upward spring is gradual but when the pull ofrod 13 has decreased to a predetermined extent said stresses become freeto snap the disk back to the position shown in Figs. 2 and 5.

The ears 18 are useful only in the event that the disk will not snapback to original position solely in response to the stresses therein, inwhich event the ears engage the periphery of the disk in the upward movement of rod 13 resulting from the contrac tion of tube 11, therebyapplying external forces which, together with the internal stresses,snap the disk back to normal position. However, if the disk is givenapproximately the correct initial set and ifit has the requisitestiffness and elasticity the ears are unnecessary except in case thedisk is damaged as by overheating the device.

The embodiment shown in Figs. 4 to G is similar to that illustrated inFigs. 1 to 3, corresponding parts being similarly desig nated, butdiffers in the following respects. Instead of the tube 11 beingconnected to rod 13' at the bottom, the tube seats on a nut 21 threadedon the rod; the upper end of tube 11 is not enlarged and is notconnected to plate 16, but the plate 16 is provided with an annular rib17 and the tube serves as an abutment for the disk indirectly throughbushing 22, plate 16 and rib 1 7; and no (igerhanging ears 13 areprovided on plate The operation of the second embodiment is similar tothe first except that no provision. is made for applying external forcesto the disk to restore it to cold position, its internal stresses beingsuflicient for the purpose-under normal conditions.

I claim:

1. A thermostatic device comprising an elastic sheet having a denttherein, thermostatically operated means for flexing a portion of thedent in the direction opposite to the dent flexure, said dent havingsuch depth and elasticity that said flexing sets up internal stresseswhich, when the flexing such depth and elasticity that said flexing setsup internal stresses which, when the flexing reaches a predeterminedmagnitude cause anotherportion of the sheet abruptly to move into adiilerent position, the latter portion of the sheet being free to snapinto said diflerent position and the sheet being constructed to returnto its original position solely by virtue of its internal stresses whenthe flexing force exerted by said means is' decreased.

3. A thermostatic device comprising an elastic sheet having a denttherein, thermostatic means arranged to apply oppositely directed forcesto'the sheet at spaced inter vals for flexing a portion of thedentin thedirection opposite to the dent flexure, said dent having such depth andelasticity that said flexing sets up internal stresses which, when theflexing reaches a predetermined magnitude cause the outermost portion ofthe sheet abruptly to move into a different position, the latter portionof the sheet being free to snap into said diflerent'position and thesheet being constructed to return abruptly to its original positionsolely by virtue of its internal stresses when the flexing force exertedby saidv means is decreased below a predetermined value, whereby thesheet snaps back and forth at different predetermined temperatures.

4. A thermostatic device comprising an elastic sheet having a' denttherein, means arranged to apply oppositely directed forces to the sheetat spaced intervals for flexing a portion of the dent in the directionopposite to the dent flexure, said dent having such constructed to againpass throu h said con-Q dition of instability when the exin exerted bysaid means is decreased, w ereby the outer aportion of the sheet snapsback to its origin position.

force said member at elements havlng 5. A' thermostatic devicecomprising an elastic member, abutments engageable with spaced points,two elongate diflerent coeflicients of expansion and extendingtransversely of said member, said elements being coupled together andbeing operative respectively upon said abutments and upon said memberintermediate the abutments, whereby unequal expansion of said elementsabruptly flex said elastic member to an oppositely disposed curvature.

6. A thermostatic device comprising a concave-convex elastic disk, anabutment engageable ,with the disk, and two heat elements havingdifferent coeflicients of expansion, said elements being connectedtogether and to said disk and abutment, respectively,

so that upon increase of temperature the lisk and abutment are pressedtogether, tending to flatten the disk and to store internal stresses insaid disk, whereby when the disk is flattened in predetermined degreesaid internal stresses become effective abruptly to change the curvatureof the disk.

7. A thermostatic device comprising a cupped disk, an abutmentengageable With the concave side of the disk at a substantial distancefrom the center of the disk, a tube connected to said abutment coaxiallyof the disk, a rod fast to the center of the disk and to said tube at apoint remote from the disk,

said tube being adapted to expand faster point than said spaced thansaid rod in response to increase of temperature, thereby to flatten thedisk.

8. A thermostatic device comprising a cupped elastic sheet having afree-peripheral edge and adapted to change shape abruptly cause abruptmovement of portions of said member more remote from said intermediatetemperature variations.

10. A thermostatic device comprising an elastic sheet having a denttherein so as to change shape abruptly in response to flexing forcesapplied thereto, and means having abutments engaging said sheet atspaced intervals to apply oppositely. directed forces to flex the sheet,the sheet being free to sna away from one of said abutments after 1t hasbeen flexed a predetermined amount.

Signed by me at Cambridge, Mass, this 5th day of November, 1923.

JOHN A. SPENCER.

points in response to

